Not applicable.
The present invention relates to the marking of product for tracking and identification (e.g., information purposes) and more particularly to using laser marked dual-coated product zones therefor.
There is a need to identify products with high quality bar codes and human-readable information without the use of an adhesive label. For example, welded tubular goods manufacturers (e.g., manufacturers of oil and gas pipeline pipe) desire to identify their products with human-readable data (e.g., heat chemistry of the source plate, pressure testing results, American Petroleum Institute (API) code conformation, etc.), as well as automatic identification (e.g., bar codes) for traceability and handling efficiency.
Paper labels often are unsuitable (as is the case in the aforementioned tubular goods) because they can peel off (e.g., contaminate the pipeline) and they may not be suitable for the environment (e.g., application to hot/wet/oily surfaces or pipes which will be exposed to high temperatures during subsequent coating operations). Bar codes and, to a lesser degree, the hunan-readable characters, require high contrast markings on products which have a wide range of background reflectivity (e.g. shiny to dull black pipe).
Heretofore, Nierenberg (U.S. Pat. No. 4,323,755) vaporizes a pattern (bar code) on glass CRTs for their identification. To improve contrast, the vaporized area can be coated first. Williams (U.S. Pat. No. 5,206,280) discloses a laser markable white pigment composition. Shimokawa (U.S. Pat. No. 4,847,181) proposes a dual layer label that can be laser marked. Gnanamuthu (U.S. Pat. No. 4,716,270) proposes a laser marking system where substrate is etched following laser marking of a label. Norris (U.S. Pat. No. 5,262,613) retrofits a mechanical engraver with a laser. Snakenborg (U.S. Pat. No. 4,946,763) proposes form a pattern in a metal stencil which is covered by a resist material containing a high concentration of metal powder. Resist material is removed by a laser beam to form the pattern. Honaker (U.S. Pat. No. 4,935,288) proposes a laser printable label having a coating of laser printable acrylic. Kiyonari (U.S. Pat. No. 5,063,137) proposes a resin composition for laser marking having an inonmic compound, like an anhydrous metal borate salt, and a resin. Kiyonari (U.S. Pat. No. 5,035,983) proposes a laser marking composition containing a non-black inorganic lead compound. Azuma (U.S. Pat. No. 4,861,620) proposes a pigment layer which can be marked by a laser beam. Herren (U.S. Pat. No. 5,030,551) laser marks ceramic materials coated with a transparent layer of titanium dioxide. Gernier (U.S. Pat. No. 4,985,780) proposes a two carriage assembly for laser marking articles. Robertson (U.S. Pat. No. 5,422,167) proposes a thermally-printable, high temperature-resistant coating for marlking hot bands and like metal products.
Robertson and O""Neal (Ser. No. 08/803,077, cited above) propose to sequentially coat a workpiece to be marked with a basecoat which is refractory to the beam of a laser and a topcoat and, while said topcoat still is wet or tacky, it is ablated by the beam of a laser. The laser beam reveals the basecoat and, by virtue of the visible contrast between the basecoat and topcoat, characters generated by the laser beam are revealed. There is a need, however, for a label which will survive appreciably higher temperatures than are obtained by the formulations disclosed by Robertson and O""Neal. For example, there is a need for the labels to survive 600xc2x0 F. to 800xc2x0 F. and higher temperatures for extended periods of time, such as are encountered when epoxy coating/curing the external outside diameter (OD) of pipe.
The present invention is directed to a system for marking objects for their identification which marks survive elevated temperatures of, say, up to 600xc2x0 to 800xc2x0 F., for extended periods of time. The inventive system for marldng workpieces for their identification includes a laser that emits a beam select band of radiation and a coating system for application to a workpiece to be marked. The coating system includes two coats of paint, a topcoat and a basecoat, which paints have been coated sequentially on the workpiece. The basecoat is an at least partially-cured, laser-blackenable paint which has been marked with fragile product identification indicia by the laser beam, after which a clear topcoat has been applied thereover. The laser generates fragile product identification indicia on the workpiece by its beam being directed onto the basecoat for its blackening to generate the fragile product identification indicia by the selective charring of said basecoat. The cleartopcoat seals the fragile product identification indicia. High temperature use of the label can be realized by using a siloxane or other high-temperature paint for both the basecoat and the topcoat.
The corresponding inventive method for marking workpieces for their identification starts with providing a laser that emits a beam select band of radiation. A workpiece is coated with a coat of a basecoat which is a laser-blackenable paint and at least partially cured. The at least partially-cured basecoat is contacted with a laser beam to char the basecoat to form fragile product identification indicia thereon. The basecoat then is coated with a clear topcoat and curing of the topcoat (and, if necessary, the basecoat) is effected. By this method, the fragile product identification indicia are protected by the clear topcoat while permitting the product identification indicia to be seen.
The corresponding inventive label bearing product identification indicia is composed of a topcoat and a basecoat which have been coated sequentially on the workpiece. The basecoat is laser-blackenable paint which has been contacted with a laser beam to char the basecoat to form fragile product identification indicia thereon, after which the clear topcoat has been applied over the basecoat to protect said fiagle product identification indicia.
Advantages of the present invention include the ability to rapidly mark virtually any configuration of workpiece, including curved or irregular as well as flat surfaces. Another advantage is the ability to mark both hot and cold surfaces. Yet another advantage is the ability to mark dirty and/or oily surfaces. A further advantage is the ability to mark workpieces on the factory floor with both human readable and machine readable characters. These and other advantages will be readily apparent to those skilled in the art based on the disclosure herein.